Supplementation of wild salmonids with captive-bred fish is a common practice for both commercial and conservation purposes. However, evidence for lower fitness of captive-reared fish relative to wild fish has accumulated in recent years, diminishing the apparent effectiveness of supplementation as a management tool. To date, the mechanism(s) responsible for these fitness declines remain unknown. In this study, we showed with molecular parentage analysis that hatchery coho salmon (Oncorhynchus kisutch) had lower reproductive success than wild fish once they reproduced in the wild. This effect was more pronounced in males than in same-aged females. Hatchery spawned fish that were released as unfed fry (age 0), as well as hatchery fish raised for one year in the hatchery (released as smolts, age 1), both experienced lower lifetime reproductive success (RS) than wild fish. However, the subset of hatchery males that returned as 2-year olds (jacks) did not exhibit the same fitness decrease as males that returned as 3-year olds. Thus, we report three lines of evidence pointing to the absence of sexual selection in the hatchery as a contributing mechanism for fitness declines of hatchery fish in the wild: (i) hatchery fish released as unfed fry that survived to adulthood still had low RS relative to wild fish, (ii) age-3 male hatchery fish consistently showed a lower relative RS than female hatchery fish (suggesting a role for sexual selection), and (iii) age-2 jacks, which use a sneaker mating strategy, did not show the same declines as 3-year olds, which compete differently for females (again, implicating sexual selection).

Eilers JM, Truemper HA, Jackson LS, Eilers BJ, Loomis DW. 2011. Eradication of an invasive cyprinid (Gila bicolor) to achieve water quality goals in Diamond Lake, Oregon (USA). Lake Reserv Manage. 27:194-204. We used a case study of whole-lake fish removal to demonstrate the importance of the fish community to nutrient cycling in Diamond Lake, Oregon, USA, to meet regulated water quality standards for pH, dissolved oxygen and nuisance algae. The cyprinid tui chub (Gila bicolor) was removed through a process beginning with netting and ending with a whole-lake and tributary rotenone treatment in September 2006. The lake was stocked with rainbow trout in spring 2007. Between 2007 and 2009, lake transparency increased 250%, accompanied by decreases in epilimnetic pH, total nitrogen, and total organic carbon. Mean concentrations of total phosphorus and ortho-phosphorus remained unchanged in epilimnetic waters. Chlorophyll a, phytoplankton biovolume, Anabaena biovolume, and Anabaena cell density declined. Daphnia pulicaria, a large herbivorous cladoceran virtually absent for 10 years, returned in abundance, and benthic biomass increased more than 12-fold. The project successfully demonstrated that water quality and fishery goals can be met through eradication of the invasive cyprinid. Fish populations need to be considered in some lakes to achieve water quality standards.

Biological responses to a formerly fi shless lake in the Cascade Range, Oregon (USA) were assessed through monitoring of recent changes and paleolimnological techniques to assess earlier changes. We used unpublished fi sheries reports, sediment cores, and available published and unpublished water quality data to evaluate changes to the lake. Diamond Lake has undergone four periods of fi sh introductions in the 20 th century. Rainbow trout (Salmo gairdneri) were annually released from 1910-2006, except for 1949 and 1954. Tui chub (Gila bicolor), an omnivorous cyprinid, were introduced in the late 1930s and the late 1980s, presumably as discarded live bait. Diamond Lake was treated with rotenone in 1954 which successfully eradicated the tui chub. The introductions of trout caused relatively modest changes in water quality and lake biota, whereas the introductions of tui chub caused major increases in cyanobacteria, changes in diatom community composition, reduction in transparency, increases in the proportion of rotifers, major reduction in benthic standing crop, and virtual elimination of amphipods, gastropods, and other large-bodied invertebrates. The unintended biomanipulations demonstrate the importance of an omnivorous cyprinid in promoting a series of biological responses throughout the lake food web.

Fifteen years of video census data from a fishway at Winchester Dam on the North Umpqua River, Oregon, were used to evaluate sampling designs to estimate abundance of spring‐ and fall‐run Chinook Salmon Oncorhynchus tshawytscha, summer‐ and winter‐run steelhead O. mykiss, Coho Salmon O. kisutch, and Pacific Lamprey Entosphenus tridentatus. Five probabilistic sampling designs were evaluated via simulation, with variation in the number of days and the number of hours within a day that were sampled over a 1‐year period. For most species, stratified one‐stage and two‐stage cluster designs were more accurate at estimating abundance than simple random sampling designs. There was very little gain in accuracy beyond sampling 8 h per day for all species. The stratified two‐stage cluster nonuniform probability design was more accurate than the stratified two‐stage cluster uniform probability design at estimating the abundance of steelhead, spring Chinook Salmon, and Coho Salmon, whereas using uniform probabilities resulted in more accurate estimates of abundance for Pacific Lamprey and fall Chinook Salmon. Additionally, the stratified and nonuniform probability designs can be adjusted for high‐priority species through allocation of the sample and assigning selection probabilities of secondary sampling units that optimize efficiency for those species. The consistency in patterns observed among species suggests that the results of this study can be applied to other systems where the abundance of multiple species is of interest. Received December 5, 2014; accepted March 28, 2015

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